Boron trichloride as a selective demethylating agent

Perylenequinone Natural Products: Evolution of the Total Synthesis of Cercosporin

“…In order to utilize this path b strategy (Scheme 2), a selective cleavage of the C2,C2’-methyl ethers vs. the C4,C4’,C6,C6’-methyl ethers was required to permit formation of the methylidene acetal. Encouragingly, aryl methyl ethers ortho to carbonyls (such as, the C2,C2’,C4,C4’-methyl ethers of 16 ) can be selectively demethylated with relatively mild Lewis acids in the presence of unactivated aryl methyl ethers (such as, the C6,C6’-methyl ethers of 16 ) 10. …”

Total Synthesis of Cruentaren A

“…This could be achieved with boron trichloride in dichloromethane at À80 8C (Scheme 4). [23,24] Besides cleavage of the methyl ether, we also observed some cleavage of the silyl ether in the b-hydroxyamide part of the molecule. The mixture of the two compounds 18 a and 18 b was then treated with the HF·pyridine complex [25] in THF, starting at À80 8C.…”

Studies in the usnic acid series. VII. The biodegradation of (+)-usnic acid by a Pseudomonas species. Isolation, structure determination, and synthesis of (+)-6-desacetylusnic acid

“…In the mass spectrometer this compound revealed fragmentations typical of the usnic acid series (40) On the basis of spectral data this product was assigned the dibenzofuran structure 9. Reaction of 8 with anhydrous aluminum trichloride (43,44) permitted the isolation of 10 in 34% yield, whereas boron trichloride (45)(46)(47)(48) in dry dichloromethane produced an 81% yield of the same component. …”